Recovery of liquid hydrocarbons from high pressure wells



Pl'l 17, 1945. c. G. KIRKBRIDE. 21,374,104

RECOVERY OF LIQUID HYDROCARBONS FROM HIGH PRESSURE WELLS Filed July 5, 1940 Patented Apr. 17, 1945 n RECOVERY 0F LIQUID HYDBOCABBONS FROM HIGH PRESSURE emmer G. xii-male, Galveston', Tex., assigner to Pan American Refining Corporation, .New York; N. Y., a corporation of Delaware I Appliesiien July 5, is'io, serial Ne. aimais f (ci. ca -115.5)

3Claims.

This invention relates to the recovery of liquid hydrocarbons from high pressure wells and more particularly to improved methods for economically recovering lightliquid hydrocarbons from well iiuids produced at high pressures and having gas-oil ratios.

In recent years advancesin the art of o well drilling have made possible lthe discovery of productive formations .at increasing depths and as a result certain fields have been found in which the well fluids produced are characte by high pressure, high gas-oil ratios and t presence of little if any heavy hydro'` carbons such as those usually associated with the term crude oil. The wells producing such uids are ordinarily called distillate wells and the lightl liquid hydrocarbon constituents recovered therefrom are known as The reservoirs from which distillates are pro- 20 1500 pounds per square inch and are usuallyl duced are invariably at pressures in excess of at pressures ranging from 3000 pounds per square inch to: sooo mas pea square men or' more, and it is believed that in-mostcases the hydrocarbons therein exist in a single phase. Whether or not this is true. a relatively small amount of liquid is generally presentin the well fluid at the well head, probably due to pressure and temperature drop through the tubing. and

s can be separated at that point. It is customary. however, to reduce the' pressure of the th orI without cooling to a relatively low v ue, e. ig; 500 to .800 pounds per square inch, emi separate the liquid distillate from the residual gas. This procedure does not give the maximum yield of Adistillate which is obtainable from thewell fluid and, unless the residual gas 'is returned tothe reservoir, gradually lowers the reservoir pressure, 80. that more and more of the valuable heavier hydrocarbons are precipitated in the formation and consequentLv 'are lost. Needless to say the compression of the enormous quantities of residual gas involved from separator' pressure, e. g. 500

'pounds Der square inch, to a pressure sufficient to cause it to re-enter a reservoir ,at 2000 pounds per square inch or incre is extremely expensive.l

It hasbeen proposed to'overeome this obstacle bycarrying out the distillate separation at pressuresin sureinthepr'esenofadditionalquantitiesof liquidhydrocarbonssimilartodlstllltabuttbis ,givesa'lowyieldofdistillatesinee the neighborhood ofwellhead pres-l bon mixture is vaporized'dueto'the phenollle? A non known as retrograde vaporization.

I have found .that maximum recovery of distil1atecan -be obtained by contacting the well fluid at avpressure of atleast 1500 pounds per square inch and' preferably at ,f a pressure approaching well head pressure with a relatively heavy absorption medium and then removing the recovered distillate from-the rich absorp` tion medium. In this way increasedy yields of distillate are obtained and the residual gas is available for recyclingto the reservoir ata very high pressure a'nd can be compressed for that purpose'at a relatively low cost'.

The method'of recovering distillate byhigh A pressure absorption. is described and claimed in my. co-pending applications. 151.243,94?,

tiled December 5, 1938. of which, the `present 'ap-' l plication is a continuation-impart. l l

critical temperatures are most desirable'forthe reason that the .ability ,of such mediato ab- Particularly'suitable absorption media.y are those which are miscible with hydrocarbons and have critical temperatures labout j70QP F. and preferably above 800 F.- Media/having. high sorb relatively heavyhydrocarbons and reject methane `increases with increasing criticaltemperature." In other words, methane has a higher equilibrium. constantand the desirable` liquidhydrocarbons have lower equilibriumponstants inthe presence of absorptionmediahaving high critical. temperatures gas-@compared with the equilibrium constantsof these materials. inthe presence of ordinary absorption oils.. This fact makes it possibieto obtain Aexceptioi'rally .good yields of distillate andalsoto operateat ver.:

.fhigh pressures..

Another factor easily seperated fromthesesiredjdistiuete by distillation, particularly'AA when the media u'sed have narrow boiling ranges. f one other important pointin connection high pressure absorption operation is `that `the abwrption mediumshould haveV a's low 'amolecular weight vas possible'consistent withy high stephen eenbeebtsined withy less este a molecular basis andthesame degree of abrption medium when it vhusa lower weight.

`lsatelitedistillate I' have found that theabsorptionmediabest n operation" byeab.- ,athighpressuresmulchof theaddedliydrocai sssoi'pmundorpressuresofatleast 1500m n.favor of absorption media having high criticalftemperatures. is l that they also have high boiling *.-pOlnts are thus more ing naphthenic and hetcrocyclic ring structures can be used advantageously.

It is an object of my invention to provide a more economical method of recovering valurable liquid hydrocarbons from high pressure well iiuids. Another object is to provide a proc- 'ess for recovering light liquid hydrocarbons from high pressure wells whereby the residual gas is available for reinjection into the producing formation without excessivey compression costs. Still another object is to provide a high pressure absorption method for the recovery of distillat utilizing a relatively heavy absorption medium having a high critical temperature. A further object is to provide a process of distillate recovery whereby Vthe valuable heavier hydrocarbons are absorbed at pressures in the neighborhood of well head pressures in an absorption medium comprising predominantly cycylic compounds having the property of preierentially absorbing such hydrocarbons from a well uuid. Further objects` and advantages of my invention will be apparent from the folmatic type, although certain compounds havj tion medium used can be for example a. petroleum fraction rich in cyclic hydrocarbons and having a critical temperature above about 700 F., but those having critical temperatures above about 800 F, are even more desirable for the reason that the ability of such media to absorb relatively heavy hydrocarbons and reject methane increases with increasing critical temperature. Oils containing relatively large proportions of aromatic hydrocarbonsl are therefore much preferred to other typesof cils. In general, aromatic compounds having critical temperatures lowing detailed description read in conjunction with the drawing which represents schematically a. suitable apparatus for practicing my invention.

My invention brieily stated comprises the absorption of the heavier constituents of a high pressure well fluid. in a relatively non-volatile absorption medium such as a cyclic compound or a mixture rich in cyclic compounds, which is miscible with the distillate, has a high critical temperature and iscapable of preferentially absorbing liquid hydrocarbons, ata pressure of at least 1500 pounds per square inch, for instance from 1500 to about 5000 pounds per square inch,

' and subsequently removing the absorbed hydrocarbons therefrom. Inmostl cases I prefer to` carry out the absorption at a pressure from about 2000 to about 4000 pounds per square inch. The temperature' at which the absorption is carried out can be forexample from 0 F.. or lower to about 150 F., 'but temperatures not materially greater than F. are preferred. -It is desirable in most cases to carry out the absorption at a pressure as close as possible to the well head pressure of the fluid produced although this may not always be possible, for example when the duid being processed is obtained from several wells at dierent pressures. It the .well head pressure is excessively high, for instance more than about 5000 pounds per square inch, it may be advantageous to reduce the pressure somewhat before contacting with absorption medium according to my invention. It is preferred to.

utilize at least a portion of the high pressure residual gas from the absorption step by introducing it into the same or another producing formation, but this is not an essential partei' my invention in its broad aspects and the sas may be otherwise disposed Aof i! desired.

`As an absorption medium I may use any suitable material which is. a liquid under the absorption conditions, composed predominantly of cyclic' compounds and considerably less volatile than the distillate to berecovered. The absorptures of diphenyl and diphenyl ether.

and other properties as above described are suitable absorption media. Examples are the cresols, triethylbenzene, diphenyl methane, liquid chloronaphthalenes, diphenyl, diphenyl ether, and mix- Other types of compounds having the properties specined above, for instance, quinoline, hexahydronaphthalene and decahydronaphthalene can also be used. Since it is' preferred to use an absorption medium having a relatively low average molecular Weight, for example t0 200, the eutectic mixture containing 75% diphenyl ether and' 25% diphenyl is particularly good because it has an average molecular weight slightly above and a critical temperature inthe neighborhood of 1000 F.' l

It is most advantageous to use as absorption media materials derived from petroleum which are .rich in aromatic hydrocarbons, have high critical temperatures and boiling points for a given average molecular weight, and at the same time are inexpensive. Some of these are byproducts of refinery operations having little value at present except as fuel. An outstanding absorption medium in this category is a relatively heavy cut produced in the catalytic reforming of naphthas, particularly when this operation is conducted in the .presence of hydrogen and an aromatization catalyst such as chromium oxide or molybdenum oxide on alumina. Such a. cut having an initial boiling point in the range from about 500 F. to about 600 F. and a boiling range not exceeding 100 F. to 200 F. is very rich in alkylated polycyclic aromatic hydrocarbons and is therefore an excellent absorption medium for use in practicing my invention. In addition its labsorption eiliciency at a maximum,

Many other refinery fractions rich in aromatic l hydrocarbons can also be used. For example a medium according to my invention.

fraction from a catalytic cracking process, operating either with or without "the presence of hydrogen, which dist-.illsy above the boiling range of distillate to be recovered, for instance in the gas oil boiling range, and, even better, a solvent extract of such a fraction, is a good absorption Another suitable material is a residual fraction produced by the vapor phase cracking of gas oil and the like, which fraction is preferably acid treated. These fractions also preferably have a high initial boiling point and a narrow distillation range.

Any suitable method of removing the absorbed distillate from the absorption medium can -be employed, but I prefer to reduce the pressure of the rich absorption medium to approximately atmospheric pressure in a plurality of stages to remove most of the methane and ethane therefrom, strip the distillate from the absorption medium under a relatively low pressure, and condense, and sash the aistinate to atmospheric pressure in several stages. By this means the well I from which u'id containing distillate is 10 4000 pounds per square inch through valve 2 and line 3, and passed throughv drying tower 4 which' The purpose of tower 4 is to eliminate the possibility of the formation of natural gas hydrates in the system. However, if the temperature of absorption is high enough a dryer may not be means of V line 5 into absorber 6, in which it is intimately contacted with a relatively non-volatile absorption medium according to my invention supplied to the upper portion. thereof through lin'e 1. Absorber 6 is maintained at a pressure in excess of 1500 pounds per square inch and preferably'is maintained at a pressure in the neighborhood of the well head pressure. The quantity'of absorption medium supplied may, of course, vary widely depending upon the absorption efiiciency, temperature, degree of absorption desired, etc.

The residual gas is withdrawn from the top of absorber 6 through back-pressure regulator 8 and line 9 and' is preferably compressed to a suitable 35` pressure, generally about 300-500 pounds per square inch above the well head pressure by compressor I and 'returned to the producing formation through line Il, valve l2 and input well I3.

r withdrawn 'at a pressure, for example, of 2000 to .contains alumina or other material capable of absorbing the small amount of moisture present.

square inch gauge. The portion of the rich absorptionmedium sent through valve 3d and line acts as a reiiux inthe stripper 39 to prevent loss of lean oil in the overhead product. Heat is supplied 4to the lower portion of stripper 38 by suitable means such as steam coil and the hot stripped absorption medium is withdrawn therefrom, partially cooled in heat exchanger 31 'and recycled to absorber 6 Vby means of line 4l, pump 42, heat exchanger 32 and line 1. In certain instances a cooler between heat exchangers 31 and 32 might be used to advantage.

Fresh absorption medium to lill they system is ,introduced through line 63 and -valve 44. After a period of operation it may -be desirable to re=` condition the absorption medium and this can be done by withdrawing all or a portion of it through valve and line lwhile adding fresh orreclaimed absorption medium through line 63. required. The dried fluid is then introduced .by 20 During this operation valve 41 in line 6I would be partly or completely closed. The reconditioning operation can also be continuous, a small proportion of the` circulating stream in line 6| being withdrawn through line d, distilled, acid treated or otherwise purified, and reintroduced through line .43.

The light hydrocarbons removed from the absorption medium in stripper 39 are removed overhead through line 48, condensed in condenserv Sand passed through line 50 and back pressure regulator 5I to a separatorl 52 maintained at a lower pressure, for example pounds per square inch gauge.v The gases' released in separator 52 pass through beek pressure regulator 53 and line ll into line 30 while the liquid therein is transferred by means of line through valve 55 to a separator 51 maintained at a still lower pressure such as 25 pounds per square inch gauge. Vapors from separator 51 are released to line 5d The rich absorption medium withdrawn from 40 through back pressure regulator 5B and the liqthe bottom of absorber 6` contains the-hydrocarbons absorbed from'the well fluid and is passed by means of line ldthrough lcooler l5 in which the heat of absorption is removed and valve I6 into separator I1 which ismaintained at an intermediate pressure below about 1000 pounds per square inch, for example 400 pounds per square inch gauge. Here much of the propane and lighter hydrocarbons are vaporized and removed means of pump 53 and line 513, the storage vessel shown being a field tank 65.

It will be readily seen from the above that I through line I8 and back pressure regulator I9v 5g have provided an extremely eillci'ent method for to line 20. The remaining liquid .phase is then passed through line 2l and valve 22 toa second separator 23 which is maintained at a still lower pressure, for example 50 pounds per square inch gauge. The gases flashed oi in separator 23 are 55 also sent to line 20 through line 2d and back pressure regulator 25, and the distillate is passed through line 2B and valve 21 to surge drum 28 at atmospheric pressure. Obviously separation in more than two .stages can be employed if de sired. Some additional light hydrocarbons are4 vaporized in surge drum 20 and these are with-i:

drawn through lines 29,'30 and 3l for any desired use,.for instance as fuel to supply heat to gases'in line 20 are also passed to line 3| but their low temperature is iirst utilized in a heat exchanger 32 to cool the lean absorption medium owing to absorber 6 through line 1.

The rich absorption medium is withdrawn surge drum 28 by means of pump 33. A portion of it is sent through valve 34 and line 35 and the remainder through valve 36', heat exchanger' 31 and line 38 to stripper 33 which is maintained excessive compression costs. The necessary compression for 1recycling the gas to the formation is preferably carriedgeut after the absorption step the stripper which will be described later, The. @5

but all or part of itcan be accomplished between the producing well and the absorber.

It is obvious that those'skilled in the art will be able to supply without dimculty those details which have been'omitted for purposes of simplicity, and to make certain modications .without departing'from the spirit of my invention.

While I have described my invention in con-= nection with `certain specific embodiments thereof,I do not desire to be limited thereto but only by the scope ot the following claims.

I claim: v

at asuitable pressure. for example pounds per z5 1. The method oi' recovering desirable liquefiable constituents from distillate well gas initially at a pressure at least as high as the retrograde condensation range of said ,constituents which comprises, expanding the gas' t0 a pressure within the retrograde condensation range of said constituents, countercurrently contacting the expanding gas with a relatively heavy liquid fraction containing a substantial portion of cyclic type hydrocarbon compounds, separating the resulting condensed constituents from the uncondensed gas, fractionating 4said condensed constituents in a relatively low boiling gasoline frac tion and a relatively heavy liquid fraction con, taining a substantial portion of cyclic type hydrocarbon compounds, and returning at least a portion of said heavy liquid traction to countercurrently contact the expanding gas as aforesaid, thereby raising the normal condensation pressure of the aforesaid desirable constituents.

2. The method of recovering desirable liqueilable constituents from distillate well gas initially at a pressure at least as high as the retrograde condensation range of said constituents which comprises expanding the gas to a pressure of at least about 1500 pounds per square inch and within the retrograde condensation range of said constituents, countercurrently contacting the expanding gas with a liquid hydrocarbon absorption. medium containing a substantial portion of aromatic type hydrocarbon compounds, separating the resulting total liquid hydrocarbons from Cil the uncondensed gas, fractlonating said total liquid hydrocarbons into a relatively low boiling gasoline and a relatively heavy liquid fraction aromatic type hydrocarbons to said countercurrent contacting step.

3. 'I'he method of recovering desirable liquefiable constituents from distillate well gas initially at a pressure at least as high as the retrograde condensation range of said constituents which comprises expanding the gas to a pressure of at least aboutl 1500 pounds per square inch and within the retrograde condensation range of said constituents, countercurrently contacting the expanding gas with a liquid .hydrocarbon absorption medium'containing a substantial portion of cyclic type hydrocarbon compounds having an average molecular Weight within the range between about 140 and about 200, separating the resulting total liquid hydrocarbons from the uncondensed gas, fractionating said total liquid hydrocarbons into a relatively low boiling gasoline and a relatively heavy liquid fraction containing said cyclic type hydrocarbon compounds, and returning at least a portion of said relatively heavy liquid fraction containing said cyclic type hydrocarbon compounds to said counterurrent contacting step as said liquid absorption medium.

, CHAUVIER G. KIRKBRIDE. 

